Re-etching electrotypes



Patented Aug. 21, 1951 RE-ETCHING ELECTROTYPES John Lomax, Kew Gardens, N. Y., assignor to Electrographic Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November 6, 1948, I Serial No. 58,789

2 Claims.

The present invention relates to a novel and improved process of improving the printing quality of electrotypes and other duplicate printing plates.

Objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the processes, steps and combinations pointed out in the appended claims.

The invention consists in the novel steps, processes, composition and improvements herein shown and described.

The present invention has for its object the provision of a novel and improved process of improving the quality of duplicate printing plates, such as electrotypes. A further object is the provision of a process by which the printing characteristics or tone quality of electrotypes may be corrected as desired so that the electrotypes are more suitable for printing as part of a four color set to beprinted at high speed on rotary web presses having a common impression cylinder. Another object is the provision of a process of opening up the shadow dots in a color printing plate so that the ink to be printed by such plate will trap better.

In high speed rotary, letterpress color printing, the colors last to be printed often show serious picking in the full tone or shadow areas as the etched portions between the halftone dots are not sufficiently deep in the duplicate originals or electrotypes as supplied to the printer, usually due to the original plates having been produced for printing at lower speeds or on older types of printing presses. According to the present invention, a process is provided for locally etching one or more of the plates of the color set, so that the spaces between the halftone dots are deepened to provide for better trapping of the ink as a wet coloris laid on the still wet color printed by a previous plate.

According to the present invention, the duplicate original or electrotype still bearing the thin film of silver which formed the conductive portion I of the mold in which it was deposited has the tops of the dots covered by a thin uniform film of a mordant-resistant ink, such as a topping ink. The recessed areas of the plate, that is the spaces between the dots, are then filled by rubbing the surface of the plate with a relatively inert, fine powder of a light and preferably white color, thus revealing the tone values of the plate and also serving to influence the subsequent etching operation.

Thereafter, the plate is heated moderately to about 200 F. So as to cause the topping ink to flow slightly and insure that the film of ink covers the tops of the dots without any pinholes or other unevenness. The fine powder filling the recesses in the plate also serves to prevent the topping ink while soft from flowing into the recesses or from coating the side walls of dots so as to interfere with the etching operation.

The plate is then placed face up on a cold, fiat stone, at room temperature, or other heat absorbing surface, and its surface is covered by a film of ferric chloride etching solution, such as is commonly used for etching of copper in photoengraving. This layer or'film of solution is preferably as thick as can be conveniently and easily held on the plate without damming the edges of the plate and is usually from 3 2 to 1 inch. The etching solution is allowed to remain on the plate from 4 to 10 minutes, until the plate has been opened up 'to the desired extent.

During the etching action, uniformity of etching is secured .and excessively rapid etching is prevented by maintaining the plate cold due to the withdrawal of the heat generated by the etching by the heavy stone on which the plate is supported. When the etchinghas been sufficiently accomplished, the etching solution is rinsed 011 in running water which also removes the powder, the surface of the plate is dried and powder is again applied so that the plate may be judged as to its tone value. If satisfactory, the topping ink is removed by solvent and the powder is brushed out of the recesses preparing the plate for curving and printing.

If desired, only a portion of the plate may be etched and such control vis exercised by staging the plate prior to etching. Thus, the areas which do not need etching may be covered with asphaltum or staging ink by means of a brush, as is done in photoengraving.

It will be understood that the foregoing general description and the following .detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now in detail to the present preferred and illustrative manner of carrying out the process of the invention, the plates which are particularly useful and to which the process is particularly adapted are duplicate original letterpress printing plates for halftone color reproduction, such as solid copper electrotypes produced from plastic molds which bear on their printing face an extremely .thin (usually much less than 0.0001") layer of silver. This silver was originally chemically deposited in the plastic mold and served to form the conductive face of the mold during the electrodeposition process. Such duplicate plates are customarily used in high speed rotary printing rather than original plates, as they substantially duplicate the original plates and can.he.made .innuantitynsufficient toflaccommodate the :needs er iailvertisers and others so that impressions can be run on different printing presses.

However, most printing plates for letterpress halftone are etched so as to be particularlya'dapted for printing where one or .two colors are printed and the third and fourth colors'aregprinte'd 'ata later time, sometimes only a 'few seconds later but often days later. During the time intervening between the printing 6f"the" first two and the last two colors of a four-color reproduction, a suflicient amount of time elapses to allow:the first two colors to set or'be absorbed slightly by .thepaper-so that,printing of .the third. and fourth .colors arefac'iliteite'd. "Howevenin the latest type of printing 'equipmentthe'T four colors are .usual- "1y.- printed in rapid succession so that "the .total time, required for thefpririting of the'four "color .platesfis at most -only 'one'se'c'o'nd or less. In .such" type 'of'printing. it is found that ithe'qua'n- "tity of ink laid -on "the 'pape'rby the first two plates is so great that the ink'carried'by thethird .and fourth plates and which .should gprint in superposition on thefirstz andsecond impressions Idoes"notitrapjproperly' andtherquality Oftheim- "pressions isinot asj goo'das expected.

'Accordin'g'ito the .present inventionfthe plates,

or: some Ofthem'Ttd'beZprintedinthismannerare .treated so "as'ftoiincrease"the .depth of the recesses between. the"dots,iparticularly: in the fulltone and shadow :areas or :the plate, without ,greatly. reducing the areaiofztliefdotswhich would correspondinglychange the intensity of the -tone printed by that portion .df :thefplate. The finished. duplicate. electrotype stillibea'ring the silver layer onits printing face"is=placed on a flat surfaceian'd isilightly' inked by means'of"ai'relatively Ihar'd inking roller,andfforlthispurposethe inking, roller' is charged with a"topping ink"which isJa relativelysoft,,acid resistant ink'iwhich can beiapplied to 'thef'tops "only of the dots and will form an acid-resistantfllm thereon. "The 'plate then powdered withisomejrelatively' inert nonabrasiveipowder ofia light'color; such as'magnesia sothatthe recessesof" thefplate' are; filled. When :the excess powder hasibeen removed, thejfplate if 'gentlyheate'd toaruniform'temperature or about 200" F. which 'causesthe"-'topping ink'ito soften and flow slightly thereby insuring thatfthe .tops of the dots 'are' uniformly-covered without pinholes, which'wouldicause' the; printing surface "of "the plate .to be "injured 'during "the etching operation.

After this mil'dburning in operation, the plate .is cooled and placed onia "relatively cold, fiat, heat-:absorbing' surfacesuchfas a thick, flat stone -atiroom temperature. "The upper j printing sur- 'face'of 'theplate: is" level "and is then flowed with a full strength etchingsolutionfofaqueousi'ferric chloride which is held'iby the surface of the .plate so long as'the "film or layer of 'etching' solution 'is *not too thick. For thisgpurpose, the layer of solution is usually from [3 to 3 inch" and is allowedtoremain"onthegprinting surface of the 'p-late for-a period offrom four to'ten minutes, or until the plate i has been "etched 'sufficiently 'to J deepen the "recesses to the :desired extent.

The action of "the; aqueousf ferric chloride'soluprinting value.

tion in combination with the relatively inert powder filling the recesses in the plate serves to moderate the action of the etching solution or mordant, also serves to prevent excessive undercutting of the dots thereby deepening the dots without excessively reducing'their area and their The -relatively ,inert filling powder also serves duringthe bumingin or heating operation to absorb any of'the topping ink which might otherwise flow over the edges of the dots and tend to coat the sides of the dots or Irun into the bottoms of the recesses. particularly important inasmuch as the largest This is dots receiveaicorrespondingly larger amount of inkduetoltheingreater area and are surrounded by the smallest recesses, while the smallest dots .arexsurrounded by the largest recesses which are *ciently, the plate is *quickly "rinsed in trunning water, which notonly'removestheferric"chiori'de etching solution, but also'washesoutthe'magnesia from the recesses of "thepririting face of the plate. The"plate is then *dried'and *againpowdered with the light coloredpowder 'sothatits printing quality may beju'd'ged'by'the etche'r and if the desired correctionmasbeenaccomplished, the plate is "again washedand' topping .ink is removed fromthe printin suffacbymeans'of a solvent; such as xylol; thereby rendering the, plate ready for curving "an'diplacing "on the ;press for the printing "operation.

Theresult "of 'the etc'hingfprocessthus carried out is to increase the depth of the' recesses between thehalftone .dotsarfd to isllglitly're'du'ce the area of the fulltoneand'shadowdotsso that the ink tobe carried by them'will"properly'trap with the previously printed colors.

If desired to treat only certainfpo'rtions of the plate in the mannerofthe'preserltprocess, the remainder of the :plate "may be protected "by means of 'a stagingsolution, asinjphotoengraving, such'a' solution usual1y"be1ng athin' solution of asphaltum dissolved I in xylol 'and applied "to the portions of the plate notto'be tchedby means of arinebrush, this'application; preferably being madebefore the; application oftheito'pping ink to the printing surfaceof theplate.

While topping ink isjpreferredi'for' the rollingup operation, other soft, "somewhat thermoplastic and acid ormorclant 'resi'sta'ntllnks' whichcan be uniformly:applied' may bel-used. 'Also,. other. powders than magnesiamay be used, such .povfders being preferably of a light color tocontrast with the'surface of the .plate, and being of an absorbent and relativelyinertcharacter so that they will absorb any flow of iexcess'i'nk and will-not be rapidly acted 'onby the etching agent. Other mordants or etching solutions than aqueousfferric chloride may. also be used so longas their reaction with the metal of the plate does not result in' the production of an excessive amount of gas. However, ferric chloride ispreferred as it=is readily available at a moderate price and thezetchers are actcustomed to the .speed 4 and uniformity of its ac ion.

The silver coating of the plate to be etched is highly desirable as it does not prevent the action of the etching solution, although it does assist the topping ink in forming between them a more effective resist than the topping ink applied directly to the surface of the copper. For this reason, the printer will preferably be supplied with the plates still retaining their silver coating on their printing face, rather than with plates from which the silver has been removed. In this way, the printer may correct the plates to suit his own operation, and'this process may be carried out quickly and economically after it has been decided on which type of equipment the plates are to be printed.

The invention in its broader aspects is not limited to the specific processes and steps shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. The process of correcting duplicate halftone letterpress plates which comprises lightly rolling up the surface of the plate with a mordant-resistant ink, filling the recesses of the plate with a powder inert with respect to said mordant, heating the plate and etching the plate with a mordant which generates no gas during etching.

2. A process in accordance with claim 1 in which the plate is a silver-faced copper electrotype; the powder is magnesia; and the mordant is an aqueous solution of ferric chloride.

JOHN LOMAX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Smith et a1.: Photo-Engraving in Relief, pp. 209-212. Published in 1932 by Pitman 8: Sons, London.

Clerc: Ilford Manual of Process Work, published by Ilford Iantd, London, 1946, pp. 220-222. 

1. THE PROCESS OF CORRECTING DUPLICATE HALFTONE LETTERPRESS PLATES WHICH COMPRISES LIGHTLY ROLLING UP THE SURFACE OF THE PLATE WITH A MORDANT-RESISTANT INK, FILLING THE RECESSES OF THE PLATE WITH A POWDER INERT WITH RESPECT TO SAID MORDANT, HEATING THE PLATE AND ETCHING THE PLATE WITH A MORDANT WHICH GENERATES NO GAS DURING ETCHING. 